Many topical pharmaceutical products such as solids, semisolids (ointments, creams, gels), liquids and suspensions contain ingredients which may cause irritation and various inflammation symptoms when applied to the skin or mucosa.
The severity of irritation to the susceptible user may range from subclinical to mild to severe. Typical symptoms of irritation include itching (pruritus), stinging, burning, tingling, “tightness,” erythema (redness) or edema (swelling). The irritation response may be due to the direct effect on the skin of certain topical product ingredients. Many active ingredients used in topical products are known irritants or are potentially irritating, for example, retinoids, benzoyl peroxide, 5-flurouracil, hydroquinone and the like.
Retinoids are a group of compounds consisting of vitamin A and its derivatives which are very sensitive to oxidative degradation and exposure to visible light. Retinoids are effective as keratolytic agents. They are used topically to retard and ameliorate photoaging of facial skin, to treat actinic keratosis, acne vulgaris, psoriasis and warts. The main drawback of retinoids topical products, and more particularly of products including tretinoin, is skin irritation.
Hydroquinone is a reduced quinone, well-recognized as a skin-lightening agent. When topically applied, it produces a reversible depigmentation of the skin by inhibiting the enzymatic oxidation of tyrosine to 3,4-dihydroxyphenylalanine, as well as suppressing other metabolic processes of melanocytes. In a clinical setting, hydroquinone is employed to treat hypermelanosis. Hydroquinone is considered an irritant in topical applications.
Benzoyl peroxide is an antibacterial agent with demonstrated activity against Propionibacterium acnes. This action, combined with the mild keratolytic effect of benzoyl peroxide is believed to be responsible for its usefulness in acne. The main side effects of benzoyl peroxide topical formulations are redness, dryness or peeling of skin, burning and itching, and swelling.
5-Fluorouracil is an antineoplastic antimetabolite. 5-Fluorouracil interferes with the synthesis of deoxyribonucleic acid (DNA) and to a lesser extent inhibits the formation of ribonucleic acid (RNA). 5-Fluorouracil is used for topical treatment of multiple actinic or solar keratoses. In the 5% strength it is also useful in the treatment of superficial basal cell carcinomas when conventional methods are impractical, such as with multiple lesions or difficult treatment sites. The use of compositions comprising 5-Fluorouracil may cause scaling, swelling, urticaria and skin rash.
Several attempts have been made to reduce the undesirable side-effects of the above active ingredients. Thus, for example Retin-A Micro® (tretinoin) 0.1% gel, Differin® (adapalene) gel, Efudex® (Valeant) (fluorouracil) solution and cream and EpiQuin™ Micro. However, none of these are products is completely satisfactory, so the search for a better product is still on.
It will be advantageous to prepare a composition for topical application having good stability, which will reduce irritation of the skin or mucosa.